Very much an interesting idea for “spectroheliographers” ! I’m going to be concentrating on the blue portion of the spectrum with higher spectral resolution. I’d be interested (and able) to catch these emission events. Thanks for the reference.

Quark is 3968.5 by factory at 0 tuning (I do not know with how much tolerance) 5A wide and max tuning range is of 0.5A both sides of CWL, may be that some redshifted units can actually be tuned on the strongest Fe(II) line although the large BP makes the device not selective. I did not noticed much difference between the extreme tuning positions but given Apollo's suggestion I will investigate this further.

Just an observation that the results published in this paper were captured at a spectral resolving power of 850000 ! That’s a fwhm bandpass of about 0.005 Angstroms (5 milliAngstroms) at this spectral line. It doesn’t seem to be necessary to use such high resolving power. But, if you look at figure 1 of the paper, the Fe emission line appears to be less than 0.1 Angstroms in width. There’s no way this line can be isolated with a standard etalon filter.